The present invention generally comprises a method of operating a hybrid electric vehicle. More particularly, the method comprises an operating mode for controlling the engine of a hybrid electric vehicle. Most particularly, the method comprises an operating mode for automatically stopping and restarting the engine of a hybrid electric vehicle in conjunction with a silent mode of operation.
An HEV is a vehicle that has a propulsion system that consists of at least one electric motor or electric machine in combination with at least one other power source. Typically, the other power source is a gasoline or diesel engine. There are various types of HEVs depending on how the electric motor(s) and other power source(s) are combined with one another in order to provide propulsion for the vehicle, including series, parallel and compound HEVs.
Various hybrid powertrain architectures are known for managing the input and output torques of various propulsion systems in HEVs, most commonly internal combustion engines and electric machines. Series hybrid architectures are generally characterized by an internal combustion engine driving an electric generator which in turn provides electrical power to an electric drivetrain and to an energy storage system, comprising a battery pack. The internal combustion engine in a series HEV is not directly mechanically coupled to the drivetrain. The electric generator may also operate in a motoring mode to provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy by also operating in a generator mode to recharge the battery pack.
Parallel HEV architectures are generally characterized by an internal combustion engine and an electric motor which both have a direct mechanical coupling to the drivetrain. The drivetrain conventionally includes a shifting transmission to provide the necessary gear ratios for wide range operation.
Electrically variable transmissions (EVT) are known which provide for continuously variable speed ratios by combining features from both series and parallel HEV powertrain architectures. EVTs are operable with a direct mechanical path between an internal combustion engine and a final drive unit thus enabling high transmission efficiency and application of lower cost and less massive motor hardware. EVTs are also operable with engine operation mechanically independent from the final drive or in various mechanical/electrical split contributions (i.e. input split, output split and compound split configurations) thereby enabling high-torque continuously variable speed ratios, electrically dominated launches, regenerative braking, engine off idling, and two-mode operation.
The development of new HEV powertrain architectures also facilitate the development and implementation of novel vehicle operating methodologies that utilize the novel features available in these systems. New operating methods are desired that utilize HEV powertrain architectures, for example, to provide vehicle operating methodologies that are particularly adapted to their operating environments, or that meet legal, regulatory or other constraints that are imposed upon their operating environments, such as by using novel combinations of electrical and mechanical propulsion energy to minimze vehicle emisssions, such as noise and exhaust emissions. It is also desirable that such operating methodologies are incorporated into the vehicle hardware and software systems as novel operating modes that are available for selection manually by an operator, or for automatic implementation by the vehicle in response to predetermined conditions.
Complex EVT HEVs utilize one or more electric machines and require advanced, high energy density, energy storage systems (ESS) which include batteries, ultracapacitors or combinations thereof, to supply electrical energy to and receive and store electrical energy from these machines. The implementation of new operating methodologies, place increased demands on the electric machines and ESS associated with the dynamic flow of power into and out of the ESS.
Therefore, it is highly desirable to develop vehicle operating methodologies that are adapted to vehicle operating environment requirements and that can be incorporated into the vehicles as operating modes that implement advance control of HEV systems, including the engine, electric machine and ESS systems.
The present invention is a method of providing an engine stop and restart mode of operation for a hybrid electric vehicle having an engine that is operatively and selectively coupled to an electric drive motor and transmission, comprising the steps of: (1) defueling the engine and maintaining rotation of the engine by rotation of the electric drive motor at a vehicle speed that is less than a vehicle stop threshold value; (2) decoupling the engine and transmission in response to a first predetermined vehicle operating condition and stopping the rotation of the engine using the electric drive motor to apply a torque to oppose the rotation of the engine; (3) restarting rotation of the engine in response to a second predetermined vehicle operating condition using the electric drive motor; and (4) recoupling the engine and transmission.
The predetermined vehicle operating conditions associated with the stop mode may be any vehicle conditions associated with the desired engine stop and restart, but preferably may be the opening and closing of the vehicle door.
This method provides significant and readily appreciable advantages and benefits associated with a substantial reduction of both noise and exhaust emissions within the stop zone of its use.